The use of dispensers for air treatment, which utilize capillary action, typically by means of a wick, to draw volatile liquid materials from a reservoir isolated from the atmosphere to a surface from which said volatile liquid materials can emanate into the atmosphere, have long been known in the art. Wicking devices are described in U.S. Pat. Nos. 1,994,932; 2,597,195; 2,802,695; 3,550,853; 4,286754; 4,323,193; 4,413,779; 4,454,987; 4,739,928; 4,913,350; 5,000,383; 5,749520; and 5,875,968; incorporated by reference.
For further discussion "emanating composition" is defined as the composition located immediately at the evaporative surface, i.e. it constitutes the composition which can be olfactively perceived. This is in contrast to the composition in the reservoir, which for definition purposes can be called "reservoir composition".
Dispensers of the prior art operate well for single component liquids or multi-component liquids, which form an azeotropic mixture. However, liquids having multiple components of differing volatility cannot be disseminated from prior art dispensers, without a change in emanating composition during the life of the dispenser. The change in the emanating composition is typically reflected by a reduction in weight loss per time unit during the life of the dispenser, as the less volatile components of the liquid accumulate at the evaporative surface, thus progressively lowering the overall vapor pressure (Raoult's Law). This is also commonly referred to as wick blockage. Since the composition in the reservoir essentially remains the same, there is an increasing discrepancy between the composition in the reservoir and the emanating composition, which evolves at the evaporative surface during the life of the dispenser.
With respect to fragrance compositions intended for air treatment this is a formidable problem. Typically, fragrance compositions are very complex mixtures of components having vastly different vapor pressures. The greater the difference in vapor pressure among the components, the more obvious will be the change in the emanating composition. E.g. this is especially true for lemon notes, which typically contain a high concentration of rather volatile components (top notes). The challenge for the perfumer then becomes to create a fragrance composition, which not only provides a balanced and pleasant emanating composition initially, but which remains balanced and pleasant despite the progressive changes during the life of the dispenser.
Changes in odor character are less of a problem for notes, which do not require a high amount of top notes, because the emanating composition does not change as drastically. Yet, less volatile components still accumulate on the evaporation surface relative to more volatile components, so that the emanating composition becomes less impactful, i.e. the air freshener becomes weaker over time.
Examples of prior art suggesting solutions to this and related problems are as follows: Bjorksten (U.S. Pat. No. 2,529,536, issued on Nov. 14, 1950) proposes to invert the wick periodically to keep it from clogging up. Bulloff (U.S. Pat. No. 2,905,591, issued on Sept. 22, 1959) as well as Ohara et al. (U.S. Pat. No. 3,903,022, issued on Sept. 2, 1975) teach the use of materials of similar vapor pressure; Similarly, Lazier (U.S. Pat. No. 2,710,825, issued on Jun. 14, 1955) teaches the exclusion of highly volatile components to impart a more constant odor character during the life of a dispenser. Lanzet (U.S. Pat. No. 2,927,055, issued on Mar. 1, 1960) recommends the use of a gelling agent in water to equalize the evaporation rates of components of a liquid, which are otherwise dissimilar. Sekiguchi et al. (U.S. Pat. No. 3,679,133, issued on Jul. 25, 1972) teach the use of pressure in lieu of a wicking action to deliver volatile liquids to an evaporation surface. Miller/Miller et al. (U.S. Pat. Nos. 5,749,519, issued on May 12, 1998 and U.S. Pat. No. 5,875,968, issued on Mar. 2, 1999) utilize the non-porous wicking action of a dual container, where the sidewalls are in a capillary spacing proximity, to deliver liquids to an evaporation surface. Compton et al. (U.S. Pat. No. 4,323,193, issued on Apr. 6, 1982) teach the use of an evaporation matrix which has a very large surface compared to the weight of liquid it can hold. In addition, the authors suggest limiting the amount of very volatile components to less than 25%, while the amount of low volatility components should be limited depending on the wick holding capacity.
Either these approaches limit the choice of components to those of similar volatility or they attempt to defy the physics of the liquid to be evaporated, since any composition having components of very different volatility will gradually change into an emanating composition with less components of high volatility and more components of low volatility during the life of the dispenser.
Sullivan et al. (U.S. Pat. No. 4,158,440, issued on Jun. 19, 1979) teach to group components of a liquid according to their volatility and to dispense each group by a separate dispensing means. This approach provides a more constant emanating composition over a long time period, even if the original liquid comprises components of different volatilities. However, within each group, the less volatile components increase in concentration over time relative to the more volatile components. Moreover, using multiple separate dispensers may be less economical than a single dispenser. Finally, the group comprising the most volatile components could exhibit a dangerously low flash point.
De Laire (U.S. Pat. No. 4,413,779, issued on Nov. 8, 1983) teaches impregnation of the evaporation surface with an agent, the evaporation rate of which is chosen, relative to the rate of deposition of the less volatile components of the air treating composition, to result in an even dispersion rate over a desired operating period. This approach addresses the problem of decreasing weight loss per time unit associated with air treatment dispensers of the wick type, but fails to eliminate the gradual change the emanating composition undergoes.
There remains a need for a well designed air treatment composition, which can deliver a constant emanating composition throughout the entire life of the dispenser without any limitations to the choice of components with respect to their volatility.
Accordingly, it is an object of this invention to provide a constant emanating air treatment composition throughout the life of an air treatment dispenser of the wick type.
It is another object of the invention to provide two corresponding air treatment compositions; one of the two compositions is used to impregnate the wick of the air treatment dispenser of the wick type, while the corresponding second composition serves as a replenishing fluid, typically provided in a reservoir, which the wick is in contact with.
It is a further object of the invention to provide a mathematical equation, which describes the relationship between the two corresponding air treatment compositions.
Other objects and advantages of the present invention shall become apparent from the accompanying detailed description of the invention.